1. Field of the Invention
This invention relates generally to optical data storage and retrieval for computer applications. More specifically, this invention relates to a pickup head that includes a holographic optical element for use in computer systems including optical disk storage.
2. Description of the Prior Art
The use and demand for compact disk devices is currently growing. Compact disk devices are found in more consumer-oriented products such as home entertainment systems, multi-media systems and CD-ROM for computer memories and other sophisticated computer devices. Optical disk memories are also emerging as an important and reliable form of information storage for computer systems generally. The optical pickup head is a key component within such devices.
An optical pickup head is typically comprised of a laser diode that is used to transmit light in a manner that allows the information from the optical disk to be retrieved. Optical pickup heads typically include a lens and a small optical system that collect and process light that originates from a laser diode and is reflected from the disk surface. Typically, a set of photodetectors that convert reflected light into electronic signals are used in order to gather the information that is stored on the optical disk. Photodetectors are also typically used to insure that the light emitted from the laser diode is focused and tracking properly.
Several conventional systems include holographic optical elements. The holographic optical elements are typically used to direct light reflected from the disk onto a set of photodetectors. In such systems, the orientation and geometry of this system, specifically the arrangement of the holographic optical element relative to the photodetectors, is crucial. A specific interaction between the holographic optical element and the photodetector elements is critical to the performance of the pickup head because of the photodetectors are used to determine proper focus and tracking. If a specific and highly specialized orientation is not maintained between a holographic optical element and the photodetectors, there is a possibility for inaccurate processing of information from the optical disk.
The geometric or alignment requirements in such systems has several drawbacks. First, stringent specifications and requirements are imposed when manufacturing such systems. Such specifications make such pickup heads difficult and relatively expensive to manufacture. Further, minor, relatively undetectable changes in a specific alignment can occur over time, which may reduce the integrity of the system. This introduces potential further cost with the need for replacement of parts or repair of the pickup head system.
Therefore, it is an object of this invention to provide a pickup head design that reduces the alignment and specific geometric tolerance requirements of individual components within the pickup head without sacrificing the performance of the pickup head. A pickup head designed in conformance with this invention provides improved economies in manufacturing by reducing the complexities associated with assembly and reducing the number of parts included in the system.